Towards development of a novel low-temperature plasma sterilizer : effects of nitrogen gas plasma on bacterial macromolecules and toxins.

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To develop a novel low-temperature plasma sterilizer using purenitrogen(N_2) gas as a plasma source, we evaluated bactericidal ability of a prototype apparatus. The decimal reduction value of the biological indicator of Geobaclllus stearothermophilus endospores was determined as 1. 9 min. Staphylococcus aureus and Escherichia coil were also exposed to the N2 gas plasma and confirmed to be inactivated within 30 min. Through the evaluation of bactericidal efficiency in a sterilization bag, we concluded that the UV photons in the plasma and the high voltage pulse to generate the gas plasma were not concerned with the bactericidal effect of the N2 gas plasma. Bactericidal effect might be exhibited by activated nitrogen atoms or molecular radicals. Endotoxins from Gram-negative bacteria were inactivated more efficiently than the autoclave treatment. Moreover, the biological activities of endotoxins also decreased significantly. The Ames test indicated that mutations induced by the plasma irradiation were negligible.